Layer-type transformer-winding cooling factors derived from analogue solution of the governing equations

The thermal problems associated with the design of layer-type h.v. transformer windings are outlined, and the concept of ‘fully developed’ thermal and hydrodynamic conditions is introduced. The equations governing the distributions of interlayer temperature and duct-oil velocity are derived for these conditions. The effect of the thermal field on oil density and viscosity in determining the velocity distribution is taken into account.The resistance-network analogue computer used in the iterative solution of the equations is described, and the procedure is explained. The results thus obtained for a particular case are compared with test values. When the test values represent significant departure from fully developed conditions, a correlation method can be employed that gives satisfactory agreement between analogue and test results within the limits of accuracy claimed. Methods for improved accuracy and further application are indicated.